Field of the Invention
The invention relates to a recto and verso printing press. A recto and verso printing press of the general type according to the invention described herein has been disclosed in the published German Patent Document DE 3605523 C2. The printing press possesses a turning device having grippers which are arranged on a gripper shaft in a turning drum and can be changed over from recto or first-form printing to recto and verso or first-form and perfecter printing. In recto printing, the sheet to be printed is clamped between a fixed gripper pad and a main gripper. In verso printing, in order to pick up the trailing edge of the sheet, the main gripper, together with an auxiliary gripper arranged at the side of the main gripper, pivots towards the trailing edge of the sheet and clamps the latter between the auxiliary gripper and the main gripper, which has been widened on one side. After a returning pivoting movement towards the gripper pad, the sheet to be printed is placed on the pad again, clamped by the main gripper, and the auxiliary gripper is lowered into a waiting position.
A considerable disadvantage of the heretoforeknown turning device is that, as the auxiliary gripper is closed in relation to the main gripper, there is an introduction of force which is off-center relative to the main gripper support, causing a tilting of the main gripper (due to shaft play). After the return pivoting and the placement of the sheet on the gripper pad, the introduction of force changes from the center of the auxiliary gripper to the center of the pad.
A result thereof is a return or backward tilting. The continuous alternating tilting leads firstly to increased wear on the bearing points and secondly to register problems, because the clamped sheets are also tilted and therefore stressed.
Starting from the aforementioned prior art, it is an object of the invention to provide a tilt-free gripper arrangement which, both in recto printing and in verso printing, operates with register-maintaining transfer and avoids premature wear, as much as possible.
With the foregoing and other objects in view, there is provided, in accordance with the invention, a recto and verso printing press, comprising an upper gripper and a lower gripper, respectively, centrally pivotable with respect to an introduction of force, the upper gripper, in recto printing position thereof, being cooperable with a gripper pad fixed to a cylinder of the printing press, the upper gripper and the lower gripper being arranged centrally in relation to one another and to the gripper pad, and having a common center line.
In accordance with another feature of the invention, the upper and the lower gripper are shaft-mounted, and the upper gripper and the lower gripper, respectively, are arranged on separate gripper supports, the gripper supports being positioned coaxially to one another.
In accordance with a further feature of the invention, the upper gripper support is of annular construction, and the lower gripper support is constructed as a solid shaft and is mounted concentrically with respect to the upper gripper support.
In accordance with an added feature of the invention, the upper gripper is actable upon the upper gripper support, and the lower gripper is actable upon the solid shaft serving as the lower gripper support and being mounted within the upper gripper support.
In accordance with an additional feature of the invention, the upper gripper support is mounted on a tube enclosing the solid shaft serving as the lower gripper support concentrically, with an annular gap being defined therebetween.
In accordance with yet another feature of the invention, the recto and verso printing press further comprises a plurality of sliding bearings arranged in axial distribution in the annular gap for mounting the lower gripper support formed as the solid shaft.
In accordance with yet a further feature of the invention, the lower gripper is threadedly secured to the solid shaft serving as said lower gripper support, via a connection part attached radially to the lower gripper support, and the connection part, with the lower gripper integrally molded on an outer end thereof, being guided outwardly through a radial slot formed in the upper gripper support.
In accordance with yet an added feature of the invention, the tube arranged between the upper gripper support and the lower gripper support is also formed with at least one radial slot through which one of the lower gripper and the connection part connected thereto extends.
In accordance with yet an additional feature of the invention, the upper gripper support comprises two axially spaced cheeks which are permanently connected to one another.
In accordance with still another feature of the invention, the recto and verso printing press further comprises a stop threadedly secured to the tube and being arranged axially between the two cheeks of the upper gripper support for limiting a pivoting movement of the upper gripper.
In accordance with still a further feature of the invention, the stop is formed with a flange thereon which serves for cooperating with the connection of the upper gripper support.
In accordance with still an added feature of the invention, the recto and verso printing press further comprises a compression spring disposed between the connection of the upper gripper support and the flange of the stop, the compression spring serving for generating a clamping force of the upper gripper.
In accordance with still an additional feature of the invention, the stop has a further flange, and an adjusting screw is threadedly secured therein, the adjusting screw serving for cooperating with the connection of the upper gripper support.
In accordance with another feature of the invention, the lower gripper is of fork-like construction and, in lowered position, encloses the gripper pad on both sides.
In accordance with a further feature of the invention, the gripper pad is of fork-like construction and has two fork prongs.
In accordance with an added feature of the invention, the lower gripper is of fork-like construction with three spaced fork prongs, and engages with the central fork prong thereof in a depression formed between the two fork prongs of the gripper pad and, with the two outer fork prongs thereof, encloses the gripper pad laterally.
In accordance with a concomitant feature of the invention, the lower gripper has a narrow shape and, overall, the two fork prongs of said gripper pad engage laterally around the lower gripper.
As a result of the central, centric association of all the gripper parts in relation to one another and to the gripper pad according to the invention, tilting is prevented, and wear and register faults are avoided.
By the novel arrangement of the fork prongs, an advantage is provided that a plurality of format widths of the sheet can be gripped, at least by one fork prong, and, therefore, exposed corners can be held as briefly as possible. The result is fewer turned-over or dog-eared corners, which could be produced by the wind resulting from travel movement during return pivoting. Furthermore, the aforementioned advantage permits a higher rotary speed of the printing press.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a recto and verso printing press, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.